Correlating structure-mechanics relationship of multiblock copolymers: Insights from molecular dynamics simulation

WH Huang and QH Chen and PW Duan and LQ Zhang and JX Shen and J Liu, POLYMER, 285, 126357 (2023).

DOI: 10.1016/j.polymer.2023.126357

Multiblock copolymers (MBCs) have garnered considerable interest in both industrial and fundamental polymer science. However, the phase structure and properties at a molecular level of MBCs remain largely unexplored. To address this, the effects of three structural factors (block number index alpha, interaction strength between hard segments epsilon H_H, and hard segment stiffness kH) on the phase structure, dynamic properties and mechanical properties of MBCs have been investigated using coarse- grained molecular dynamics (CGMD) simulations. The degree of phase separation, psi, has been quantified based on the number of neighboring beads designated to measure the phase separation structure. Results indicate that a lower alpha (longer block chain length), stronger epsilon H_H, and weaker kH significantly reduce the contacts between soft and hard segments, leading to an increase in psi. An examination of higher psi (greater than 0.7) reveals two Tg s that converge as psi decreases and eventually merge into one. Mechanical properties are improved with increasing alpha at low strains, whilst they change non monotonically at high strains, likely due to differing contributions of soft and hard segments to the stress. Systems with stronger epsilon H_H and kH exhibit superior mechanical properties due to their higher non- bonded energy increments and bond orientation. In general, the mode of the variation of phase separation structure, glass transition temperature and mechanical properties of MBCs at the molecular level, has been elucidated valuable insight for the design and synthesis of high-performance MBCs materials.

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